1. Field of the Invention
The present invention relates to an illuminating device that includes a light source body having light sources, and a lens array having lenses which correspond respectively to the light sources.
2. Description of Related Art
Conventionally, in JP-A-05-104979, for example, a head up display with a halogen lamp used as a light source is proposed. In JP-A-2005-228606, an illumination device with a light emitting diode (LED) employed as a light source of a head up display is proposed.
According to the head up display described in JP-A-05-104979, light, which is irradiated from the halogen lamp, is condensed by an integrator lens, and a front panel is irradiated with the condensed light through a light receiving display element. Then, the light which is reflected by the front panel is delivered to a surveyor (observer).
In the head up display described in JP-A-2005-228606, light that is emitted from a light source body, in which LEDs are arranged, is collected by a lens array, and a front panel is irradiated with the collected light via a liquid crystal display panel. Then, the light which is reflected by the front panel is delivered to a user (observer).
As described above, in the head up display described in JP-A-05-104979, the halogen lamp is employed as a light source. Because the halogen lamp produces light due to heat radiation, besides visible light, infrared rays (heat ray) are included in this light. As a result, the light receiving display element is irradiated with the infrared rays together with the visible light. Accordingly, there is a possibility that the light receiving display element generates heat and is thereby damaged.
To resolve the above-described problem, in JP-A-2005-228606, the LEDs are employed as a light source. Since the LED emits light having wavelength corresponding to an energy gap (value inherent in a semiconductor) of a semiconductor, when the visible light is selected as the light of the LED, the infrared rays are not contained in the light applied by the LED. Therefore, the heat generation of the liquid crystal display panel (light receiving display element) due to the light applied by the light source is limited.
When the LED is used as the light source of the head up display, the LED has lower brightness than the halogen lamp. Accordingly, more than one LED needs to be prepared. In this case, an optical system for converging light irradiated by each LED in a one direction is necessary. In JP-A-2005-228606, the above-described lens array is adopted as an optical system having such a function.
The lens array described in JP-A-2005-228606 includes convex lenses for focusing the light irradiated from one LED. A surface of the lens array opposed to the LED has a flat surface shape. A reverse surface of this opposed surface is formed in such a shape that curved surfaces (convex lenses), which project on the reverse side, are joined together (see FIGS. 3 and 4 in JP-A-2005-228606). An optical axis of the LED and a vertex of the convex lens corresponding to this LED, coincide with each other. The light concentrated by the convex lens constitutes a brightness distribution with the vertex of the convex lens being peaked. The light having such a brightness distribution is emitted from each convex lens, and the observer is irradiated with these lights through the liquid crystal display panel and the front panel.
The brightness distribution of light varies according to an observing direction of the observer. The brightness distribution of light when a direction that is perpendicular to a luminescent surface of the LED is set at the observing direction will be described below.
In the brightness distribution of light emitted from one convex lens, brightness is the highest at the vertex of the convex lens, and the brightness becomes lower from the vertex toward a boundary line, which is formed between the one convex lens (curved surface) and a convex lens (curved surface) adjacent thereto. In this manner, when the brightness rapidly changes between the vertex of the one convex lens and the above-described boundary line, a brightness difference between the lights becomes marked. Furthermore, in the lens array shown in JP-A-2005-228606, the above boundary line has a linear shape, so that a region having the lowest brightness also has a linear shape. As described above, if the observer is exposed to the light, the brightness difference of which is prominent, and which includes brightness unevenness with the lowest-brightness region having a linear shape, the observer may recognize the lowest-brightness region as a fringe.
When the observer is irradiated with the light including the brightness unevenness, which may be recognized as a fringe by the observer (such a light is hereinafter referred to as a “light including a fringe” for the sake of simplicity), via the liquid crystal display panel and the front panel, the observer cannot easily visually identify light information indicated on the front panel.
Additionally, the brightness distribution of the light delivered to the observer depends on the observing direction (i.e., sight line direction) of the observer. Accordingly, in a certain observing direction, the observer is sometimes not irradiated with the light including a fringe. Nevertheless, since the observing direction of the observer is not constant, the observer eventually observes the light including a fringe. As a result, the observer cannot readily visually confirm the light information displayed on the front panel.